Problem 65 - Chemistry: An Atoms-Focused Approach

Question

When \(\mathrm{CaCl}_{2}\) dissolves in water, which molecules or ions occupy the inner coordination sphere around the \(\mathrm{Ca}^{2+}\) ions?

Step-by-Step Solution

Answer

Answer: Water molecules (H₂O) occupy the inner coordination sphere around the Ca²⁺ ions due to strong ion-dipole interactions.

Step 1: Identify the dissociation of the salt (Calcium Chloride) in water

When \(\mathrm{CaCl}_{2}\) salt dissolves in water, it forms \(\mathrm{Ca}^{2+}\) ions and \(\mathrm{Cl}^{-}\) ions. This can be represented by the following equation: $$\mathrm{CaCl}_{2\, (s)} \rightarrow \mathrm{Ca}^{2+}_{(aq)} + 2\mathrm{Cl}^-_{(aq)}$$ Where \(s\) represents solid \(\mathrm{CaCl}_{2}\) and \(aq\) represents the aqueous ions.

Step 2: Identify the possible molecules or ions that can interact with the \(\mathrm{Ca}^{2+}\) ions in water

The two types of molecules present in this solution are \(\mathrm{Ca}^{2+}\) ions, \(\mathrm{Cl}^{-}\) ions, and water molecules (\(\mathrm{H}_{2}\mathrm{O}\)). We know that ions in water are surrounded by water molecules due to ion-dipole interactions. So, the water molecules are the candidates to form interactions with the \(\mathrm{Ca}^{2+}\) ions and to be present in the inner coordination sphere.

Step 3: Determine the molecules or ions occupying the inner coordination sphere around the \(\mathrm{Ca}^{2+}\) ions

As discussed in step 2, the water molecules are the most likely candidates to occupy the inner coordination sphere around the \(\mathrm{Ca}^{2+}\) ions due to ion-dipole interactions. The water molecules surround the ion, creating a stable hydration shell, as their oxygen atoms have a partial negative charge and are attracted to the positive charge of the \(\mathrm{Ca}^{2+}\) ion. In summary, when \(\mathrm{CaCl}_{2}\) dissolves in water, the inner coordination sphere around the \(\mathrm{Ca}^{2+}\) ions is occupied by water molecules (\(\mathrm{H}_{2}\mathrm{O}\)) due to strong ion-dipole interactions.